B12 Supplementation & Breast Milk

Results of a randomized and controlled trial were recently published in the American Journal of Clinical Nutrition, providing more detail on the efficacy and timing of B12 supplementation given pre- and postnatally in the human milk (HM) concentration of B12. Pregnant women between 12-27 weeks gestation were recruited for this study from Tanzania, an area with a high incidence of maternal and infant B12 deficiency; 30% of infants there have a frank deficiency, and another 20% have insufficient levels. In this study, 73.3% of women had low HM B12 (<310 pmol/L) at 6 weeks postpartum, and 68.4% at 7 months postpartum.

In 2018 the AJCN also published prevalence data in the U.S., though based on a small sample size. Using the same cut-off of <310 pmol/L, approximately 20% of women had low HM B12. While no significant difference in prevalence was observed between omnivorous, vegetarian, and vegan women, women who avoided meat were also much more likely to be taking vitamin B12 supplements.

In this Tanzanian-based study, supplementation included 50 ug/d B12 (a relatively high dose) or placebo, starting from recruitment through 6 weeks postpartum. This increased the HM B12 concentration by 34.4% at 6 weeks, but the increase did not persist by 7 months postpartum. Additionally, some women continued to receive B12 (or placebo) through 18 months postpartum, which increased HM B12 by 15.9% at 7 months postpartum.

While there is still much to be learned regarding the optimal timing of B12 supplementation, the optimal dose and even the optimal reference range, this study strongly suggests that high-dose supplementation can help to improve breast milk levels of B12, and that it may be necessary to continue supplementation, especially as long as women continue to provide breast milk to their infants.